It is known in the art relating to internal combustion engines to generate air swirl in the cylinders to provide enhanced combustion characteristics. Commonly used fixed geometry swirl generating inlet ports may produce the desired swirl intensity to promote combustion at part load, but they generally reduce the engine volumetric efficiency at wide open throttle and thus limit the maximum charge volume and thereby the maximum output of the engine.
Some variable geometry swirl generating ports have been proposed having various forms of vanes or other devices to vary the port configuration. However, in at least some cases, the resulting port configurations and the added valves, vanes or the like have not provided the desired combination of swirl generation at part throttle while allowing free breathing at wide open throttle and high engine speeds.